The proposal is designed to gain basic information on the anatomy and permeability properties of the rat choriocapillaris, Bruch's membrane and basal surface of retinal pigment epithelial cells. Studies will include adult animals, older animals and stages between late fetal and early post-natal development. Previous work in this laboratory indicates that the choriocapillaris is not freely permeable to larger macromolecules, but increasingly restricts their passage with increasing molecular weight and diameter. The proposed studies are to examine these properties in greater detail using addition hemeproteins and dextrans of narrow size range. Changes in permeability will be correlated with morphological alterations as viewed in freeze-fracture replicas. Intrinsic negative charges (anionic sites) on the luminal surface of capillary endothelium and in Bruch's membrane will be studied using cationic probe molecules with high isoelectric points such as cationized ferritin and lysozyme. The study will attempt to determine whether permeability properties of Bruch's membrane are based on size and electrostatic properties. Information gained from these studies will serve as a basis for investigating changes in these barriers that may be involved in the pathogenesis of retinal or vascular lesions.